1. Field of the Invention
The present invention relates to novel compositions of matter based on chlorine-containing polymer and comprising an effective stabilizing amount of a zinc stannate and/or zinc hydroxystannate.
This invention also relates to the use of the zinc stannates and/or zinc hydroxystannates as heat stabilizers for chlorine-containing polymers.
The chlorine-containing polymers to which the present invention relates are, in particular, poly(vinyl chloride) (PVC), which is the most significant commercially; poly(vinylidene chloride); copolymers predominantly comprised of vinyl chloride recurring units prepared from vinyl chloride and other monomers copolymerizable therewith; and mixtures of polymers or copolymers, a predominant proportion of which is derived from vinyl chloride.
In general, any type of PVC is suitable, whatever the process for the preparation thereof - bulk polymerization, suspension polymerization, dispersion polymerization or any other type--and whatever its intrinsic viscosity.
The homopolymers of vinyl chloride may also be chemically modified, for example by chlorination.
Numerous copolymers of vinyl chloride may also be stabilized against the adverse effects of heat, namely, yellowing and degradation. These are, notably, the copolymers prepared by copolymerization of vinyl chloride with other olefinically unsaturated comonomers copolymerizable therewith, such as, for example, vinyl acetate or vinylidene chloride; maleic or fumaric acids or their esters; olefins, such as ethylene, propylene and hexane; acrylic or methacrylic esters; styrene; and vinyl ethers such as vinyl dodecyl ether.
These copolymers typically contain at least 50% by weight of vinyl chloride recurring units and preferably at least 80% by weight of vinyl chloride recurring units.
The compositions according to the invention may also comprise mixtures based on chlorine-containing polymers containing minor amounts of other polymers, such as halogenated polyolefins or acrylonitrile/butadiene/styrene copolymers.
PVC, whether alone or in admixture with other polymers, is the primary chlorine-containing polymer comprising the compositions of the present invention.
2. Description of the Prior Art
It is known to this art that the conversion of chlorine-containing polymers, and more particularly of PVC, at elevated temperatures cannot be accomplished without the addition of heat stabilizers thereto.
Indeed, if the chlorine-containing polymer is heated to processing temperatures, objectionable coloration appears which alter its appearance, an important characteristic for numerous applications.
This disadvantage is overcome by incorporating therein stabilizers essentially consisting of metal or organometallic compounds adopted, in particular, to absorb the hydrochloric acid produced by the degradation of the polymer.
These heat stabilizers are essentially organic derivatives of zinc or cadmium in combination with organic derivatives of calcium, barium or magnesium.
They may be accompanied by other compounds, typically designated "costabilizers" or "secondary stabilizers", the purpose of which is to supplement and intensify their effect, in particular as regards the appearance characteristics of the final product.
This is the case with mixed metal systems based on derivatives of cadmium and barium, or of zinc and barium, or of zinc and calcium, which have to be accompanied by costabilizers such as epoxide compounds, organic phosphites, dihydropyridines and/or betadiketones.
Among these metal systems, those which include cadmium derivatives are becoming less and less used, because of the deleterious effects of cadmium.
The formulations of chlorine-containing polymers containing combinations of organic derivatives of zinc and barium, or organic derivatives of zinc and calcium, with organic costabilizers, are typically suitable for such applications as, for example, the production of shaped transparent rigid bottles or films for exterior use.
However, in certain instances--severity of the conditions of thermodynamic conversion, intrinsic instability of certain such polymers--it is necessary to increase the effectiveness of the customary stabilizers insofar as the appearance of the final product is concerned, and especially the permanence of this effectiveness, when the thermal stresses are intensified and prolonged.